Wednesday, February 25, 2009

I've been talking about the Chamonix workshop for the past few posts, and will spend a few more on it, mostly because I find the accelerator side interesting. Plus, ATLAS kind of depends on those protons eventually colliding ;)

Yesterday afternoon, we got a 3-hour summary of the workshop (agenda and slides), so I thought I would share some of the more interesting items. The information (and accelerator acronyms) flew by pretty quickly, so this comes with the usual disclaimer that any mistakes are mine.

The first topic is "training" the dipole magnets... For magnets, training is accomplished by gradually increasing the current through the magnet (which increases the magnetic field) until the magnet quenches. Then the current is increased again, hopefully past the previous quench point, until the magnet quenches again at a higher current and magnetic field. The magnet "remembers" how high the current got, so the next time you turn it on (days or weeks later), it should be happy with any current below the highest quench point. And by the way, the currents that we are talking about are ~10000 A (compared to your wall plug of 15-20 A).

The LHC accelerator physicists talk in terms of "number of quenches"—how many times they have to repeat this current increase to quench cycle in order to reach a given magnetic field and therefore energy. The design energy of the LHC is proton collisions at 14 TeV, which means that every magnet in the ring must be trained up to 1/2 of that energy, or 7 TeV. This fall, we are going to run at 10 TeV, so the magnets must be trained up to 5 TeV (which they are, except for the repaired magnets in the sector that had the incident last September). They would like to reach the LHC's design energy for the run in 2011.

At Chamonix, they tried to estimate how many quenches it would take to reach given energies in the magnets... keep in mind that they can train magnets in the 8 sectors in parallel, but can only do ~3 quenches per day. Their estimates are that it would take 11 quenches to reach the equivalent current for 6 TeV in each magnet, 84 quenches to reach 6.5 TeV, and nearly 1000 quenches to reach 7 TeV (design energy). 1000 quenches means training magnets for 2 months!

So you can see, it gets a lot harder to make that last step from 13 TeV to 14 TeV. Which is why 13 TeV might be the maximum center-of-mass energy reached by the LHC. But I have 2 conclusions: 1) I wouldn't be disappointed with 13 TeV and 2) I'm not going to count these accelerator physicists out just yet...

Monday, February 16, 2009

We've heard the big news about the LHC schedule that was decided in Chamonix a few weeks ago, so I was not expecting anything too exciting from a talk this morning at our ATLAS collaboration meeting. What did strike me (again) was the size and scale of the task facing the physicists and engineers getting the accelerator back up and ready to go.

For example, they had to take basically a giant Q-tip dipped in alcohol to clean the soot from the inside of nearly 2 miles of beam pipe (the soot being from the incident last September). Another number is 150 miles -- the additional length of cable that needs to be installed for the enhanced quench protection system. And how about $10 million? Compared to the stimulus package it might be peanuts, but it's the additional cost of electricity for running the LHC through next winter (electricity is more expensive in winter than summer here, which is why we would usually shut down in winter). And finally, 104 -- the number of places around the ring where they will reinforce those red blocks that anchor the magnets to the concrete tunnel floor (see the CERN bulletin).

I'm trying to keep these numbers in mind, because otherwise it can be pretty discouraging to scan back through my blog posts to see how the schedule has slipped from September 08 to April 09 to May to June to ... September? October? All because of some missing solder:

(The bad magnet connection. As I understand it, the connection on the left is "bad" because the half-circle is copper-colored, rather than coated with the silver-colored solder that you can see on the connection on the right.)

The bottom line is that I need to be patient, because they still have a ton to do to fix the machine and we have months to go before there are protons in the LHC. Good thing there are plenty of photos from fashion week to keep me occupied ;)

Thursday, February 12, 2009

So, you may have seen in Symmetry Breaking that Entertainment Tonight is broadcasting from CERN, highlighting the upcoming movie release of Angels and Demons. I read the book (CERN has an FAQ page about it) and found it pretty entertaining, even though it's definitely fiction.

Well, we were at the CERN store after lunch today and noticed a large group of reporters gathering across the street at the Globe...

and guess who came out?! Tom Hanks, Ayelet Zurer, and Ron Howard!!!

How cool is that! Ayelet Zurer looked really pretty, Ron Howard was wearing a CERN hat, and I just got to see Tom Hanks!

Monday, February 9, 2009

Expected beams in the LHC at the end of September, collisions late October. This is a 6-week delay compared to the previous schedule...

The cause of this delay is due to several factors such as implementation of a new enhanced protection system for the busbar and magnet splices, installation of new pressure relief valves to reduce the collateral damage in case of a repeat incident, application of more stringent safety constraints, and scheduling constraints associated with helium transfer and storage.

In Chamonix there was consensus among all the technical specialists that the new schedule is tight but realistic.

The new pressure relief valves will be installed in the 4 warmed-up sectors this year, and they will be installed in the cold sectors in 2010.

he sent CERN users and staff an email along with a Press Release. The contents: a recommendation for running the LHC through the winter of 2009-10 all the way to autumn of 2010, at an energy of 10 TeV (compare this to the "design" energy of 14 TeV, and the proton-antiproton energy of 1.96 TeV at Fermilab's Tevatron). This should give the experiments enough data to get our physics on :)

At this workshop (which was mostly for the Accelerator division, as I understand it only a few representatives from the experiments were invited) they also discussed the cause of September 19th incident and what they've done to detect similar potential problem spots in the machine:

Among the topics discussed in Chamonix was the underlying cause of the incident that brought the LHC to a standstill on 19 September last year. The incident was traced to a faulty electrical connection between segments of the LHC's superconducting cable. Since the incident, enormous progress has been made in developing techniques to detect any small anomaly. These will be used in order to get a complete picture of the resistance in the splices of all magnets installed in the machine. This will allow improved early warning of any additional suspicious splices during operation. The early warning systems will be in place and fully tested before restarting the LHC.

Following the incident, a further two suspect connections have been identified. One of these has now been investigated, revealing that the splice between cables had not been correctly carried out. As a result the magnet containing the second will also be removed from the tunnel for repair. Since resistance tests can only be conducted in cold magnets, three of the LHC's eight sectors remain to be tested: sector 3-4 where the original incident occurred and the sectors on either side. Within sector 3-4, the 53 magnets that are being replaced in the tunnel will all be tested before cool down, and the sectors either side will be cooled down early enough to intervene if necessary with no impact on the schedule. This leaves around 100 dipole magnets that cannot be tested until September, and a correspondingly small chance that repairs may run into currently scheduled running time.

So there's the latest dish on the machine. The "Part 1" in the title of this post refers to the caveat that the schedule recommendation needs to be approved by CERN management in a meeting today. I'll post again when we get word on the decisions that were made in that meeting, which I hope will give us a more detailed restart schedule for this year.

Tuesday, February 3, 2009

I guess I finally miss the US a bit. I don't think it was just a coincidence that this weekend turned into an homage to the US of A. So far, I've been really trying to embrace the pace, culture, and way of life in France/Switzerland. But you start to miss some things, like being able to stop by and pick up food on the way home without it turning into a 2-hour (and $$$) experience. And being able to pay $1 for a pitcher of beer while wearing rented shoes ... aka bowling ;) And watching football. So it's good to inject some bits of home here and there when you can...

On Friday we called and ordered Domino's pizza. Delivery wasn't possible to France, but we went and picked it up, saving 40% on delivery charges! It still wasn't cheap compared to Domino's in the US, but hey, we were in the mood to splurge. And later that evening, we went bowling! Granted there were no $1 (or even 1€) pitchers, but it felt like the real deal:

And on Sunday night we gathered with a bunch of other football fans to watch the Super Bowl at Pickwick's in Geneva, complete with Madden commentary (although no US commercials). The game started around midnight, and we didn't get home until 5am, but man am I glad we stayed until the end. What a game!

To finish it off with some physics, there was also an LHC update this weekend. It's pretty jargon-y, but the basic gist is that they can now identify the problem that caused the incident in September, and they found and are going to fix another magnet with the same problem (in Sector 6-7). They've also made more progress replacing the damaged magnets in Sector 3-4 (where the incident occurred).

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About Me

I'm a post-doc in particle physics at Brookhaven National Laboratory in Upton, NY. I work on the ATLAS experiment at CERN, and I am stationed at CERN for at least a year... ok more like 2 at this point...